1. Field of the Invention
The present invention relates generally to antenna feed methods, and more particularly to antennas for transmitting and/or receiving electromagnetic energy. More particularly, the invention relates to a method to feed antenna(s) in close proximity to a monopole.
2. Description of the Prior Art
Monopole antennas are known in the art and described in numerous antenna texts. U.S. Pat. No. 4,814,777 issued to Monser teaches an antenna system comprising a vertical monopole antenna coupled to a first feed on a ground plane conductor and a dipole antenna comprising a plurality of horizontal dipole antenna elements coupled to a corresponding plurality of feeds on the ground plane conductor. The plurality of dipole antenna elements being disposed about the first feed. The vertical monopole antenna comprises a plurality of monopole antenna elements, the plurality of monopole antenna elements and the plurality of dipole antenna elements being alternately radially disposed about the first feed.
U.S. Pat. No. 3,739,390 issued to Poppe, et. al., teaches a dual antenna system including first and second antennas respectively capable of operating at first and second distinct frequency ranges. The antenna system taught comprises a coaxial transmission line having a central conductor and an outer conductor surrounding and insulated from the central conductor. The central conductor of Poppe has a section that extends axially beyond the outer conductor, at least a portion of which defines a radiating element of a first antenna. A pair of intersecting conductors coupled to the outer conductor of Poppe""s antenna system extend radially for defining a first reference for element for a first antenna and also defining a radiating element of a second antenna. The pair of intersecting conductors serve as a load element for the outer element thus increasing the effective electrical length of the second antenna. A grounded sleeve surrounds and is insulated from the outer conductor and defines a second reference element for the second antenna. The inner conductor serves to feed one antenna and the outer conductor feeds the second antenna and the two antennas are fed from the same point from the ground plane.
U.S. Pat. No. 2,498,655 issued to Faymoreau, et. al. teaches an orientable antenna arrangement comprising a plurality of N superimposed antenna systems where N is the number of systems each rigidly mounted on a mast structure. The mast structure comprising in space a coaxially fixed relationship a vertical central conducting member and a plurality of coaxial tubular conducting members there being one more of the conducting members than there are antenna systems. The antennas taught by Faymoreau are each fed coaxially to each other through the same point in the ground plane.
A method to feed antennas proximal to a monopole antenna is shown. A monopole antenna is fed through a ground plane by a conventional means. A transmission feed line for an antenna proximal the monopole antenna passes through the ground plane and makes contact with the monopole antenna at some distance from the ground plane, this contact being made by a non-signal carrying conductor of the transmission line. In the special case of a coaxial feed transmission line, this non-signal carrying conductor is the outside of the outermost conductor of the coaxial feed line. After making contact with the monopole antenna the feed line then passes through or along the side of a monopole antenna to reach the antenna proximal to the monopole.
A feed method is defined herein as the method used to convey the signals from the transmitter to an antenna and to convey signals from an antenna to the receiver.
The feed method taught herein provides both a method of feeding antennas in the proximity of the monopole and helps a monopole to obtain a wider impedance bandwidth. This feed method is applicable to feeding any types of antennas that are in the proximity of a monopole. A balun and impedance matching circuit for the attached antenna, if needed, may be located either inside or outside the monopole. The specific type of monopole used is not pertinent, the monopole can be thin, thick, cage, conical, inverted conical, printed-circuit, or any other type of monopole. This method has been shown to work well with conical monopoles and inverted conical monopoles, both of solid and caged wire construction. For typical flared or conical monopoles the electrical contact point taught herein is typically located at more than 0.1 wavelength from the monopole feed point. At certain frequencies where a flared or conical monopole is approximately 0.15 wavelengths long, the presence of the electrical contact taught herein produces a higher input resistance for the monopole feed, hence assisting in impedance matching the monopole and allows the monopole height to be reduced.
The above brief description sets forth rather broadly the more important features of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contributions to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.
In this respect, before explaining the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood, that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
It is therefore an object of the present invention to provide a method to feed antennas proximal to a monopole antenna.
It is also an object of the present invention to allow that antennas in close proximity to a monopole can be used with minimum degradation of performance of either the monopole or the other antennas.
It is a further object of the present invention to improve the impedance bandwidth performance of the monopole.
It is another object of the present invention to reduce the overall dimensions of the volume occupied by the antenna system, including the monopole.
It is an another object of the present invention to provide a feed method that is relatively easy to construct and results in extremely broadband performance of the antenna system.
It is another object of the present invention to obviate the need for costly, narrowband concentric coaxial feed structures for plural antennas.
These together with still other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.